The goals of this research program are to analyze cognitive functions and to develop cognitive assessments that may identify and distinguish normal human infants and infants at-risk for developmental disability, such as mental retardation. Five studies systematically investigate four information-processing capacities in 5--6-month-old infants: habituation, recognition memory, novelty preference, and cross-modal transfer. Study 1, on psychometric characteristics, is designed (1) to assess the short-term reliability of each capacity, (2) to determine individual differences and variability in each, (3) to explore interrelations among the four, and (4) to assay how reliability and individual variability modulate with stimulus variation. Though these four capacities have been studied extensively, and their clinical utility implied, basic psychometric characteristics of the four are underresearched; moreover, they have not previously been examined conjointly in the same sample. Study 2, on origins, is designed to investigate endogenous and exogenous influences on individual differences among 5--6-month-old infants in the four information-processing capacities in terms of (1) infants' perceptual capacities at 1--2 months and (2) maternal didactic interaction styles at 1--2 months. Study 3, on concurrent correlates, is designed to determine associations between infant cognitive capacities at 5--6 months and (1) five dimensions of infant temperament and (2) maternal intelligence, socioeconomic status, and didactic interaction style. Study 4, on predictive validity, is designed to trace relations between cognitive capacities in 5--6-month-olds and their performance between 12 and 48 months (1) on the same cognitive measures, (2) on measures of language proficiency and psychometric intelligence, and (3) on associated cognitive measures like play and classification. Study 5, on clinical assessment, is designed (1) to compare cognitive capacities in infants born at-risk for cognitive disability against normal infants and (2) to establish the relative values of different indices for predicting cognitive deficit in high-risk and normal infants through longitudinal follow-up. This research addresses fundamental questions in perception and cognition, in infancy and human development, and in clinical psychology, psychiatry, and pediatrics. Answers to these questions will be of direct interest to defining the nature of cognitive dysfunction and to promoting remediation in high-risk populations of infants.